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Status

Current state:  "Under Discussion" Discarded (covered by KIP-182)

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: TBD

PR: herehere [Change the link from KAFKA-1 to your own ticket]

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Note: This KIP may become obsolete as the discussion on "Streams DSL/StateStore Refactoring" supersedes it.

Motivation

The recommended practice to create a StateStoreSupplier is as in per the following example:

StateStoreSupplier countStore = Stores.create("Counts")
    .withKeys(Serdes.String())
    .withValues(Serdes.Long())
    .persistent()
    .build();

However, StateStoreSupplier is a generic interface that take takes the store StateStore type as a parameter:

public interface StateStoreSupplier<T extends StateStore>

...

As StateStoreSupplier is passed to count/reduce/aggregate etc. methods on KGroupedStream or KGroupedTable, the compiler cannot detect that if a supplier for the wrong kind of store is provided.

...

The StateStoreSupplier argument stands out as a raw type. Making it type-parameterised will help detect prior to runtime at compile time errors such as when someone refactors their app to use a different typo of aggregations (e.g. TimeWindowed vs SessionWindowed) and forgets to change the StateStoreSupplier passed in.

Public Interfaces

...

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Rejected Alternatives

• KGroupedStream -deprecate the following methods:

  • KTable<K, Long> count(final StateStoreSupplier<KeyValueStore> storeSupplier);

  • <W extends Window> KTable<Windowed<K>, Long> count(final Windows<W> windows,
                                                                                                   final StateStoreSupplier<WindowStore> storeSupplier);

  • KTable<Windowed<K>, Long> count(final SessionWindows sessionWindows,
                                                                final StateStoreSupplier<SessionStore> storeSupplier);
    
    

  • KTable<K, V> reduce(final Reducer<V> reducer,
                                       final StateStoreSupplier<KeyValueStore> storeSupplier);
    
    

  • <W extends Window> KTable<Windowed<K>, V> reduce(final Reducer<V> reducer,
                                                                                                final Windows<W> windows,
                                                                                                final StateStoreSupplier<WindowStore> storeSupplier);
    
    

  • KTable<Windowed<K>, V> reduce(final Reducer<V> reducer,
                                                            final SessionWindows sessionWindows,

                                                            final StateStoreSupplier<SessionStore> storeSupplier);
    
    

  • <VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                                                         final Aggregator<? super K, ? super V, VR> aggregator,

                                                         final StateStoreSupplier<KeyValueStore> storeSupplier);

  • <W extends Window, VR> KTable<Windowed<K>, VR> aggregate(final Initializer<VR> initializer,
                                                                                                               final Aggregator<? super K, ? super V, VR> aggregator,
                                                                                                               final Windows<W> windows,
                                                                                                               final StateStoreSupplier<WindowStore> storeSupplier);

  • <T> KTable<Windowed<K>, T> aggregate(final Initializer<T> initializer,

                                                                        final Aggregator<? super K, ? super V, T> aggregator,

                                                                        final Merger<? super K, T> sessionMerger,

                                                                        final SessionWindows sessionWindows,

                                                                        final Serde<T> aggValueSerde,

                                                                        final StateStoreSupplier<SessionStore> storeSupplier);

• KGroupedStream - add the following replacement methods:

  • KTable<K, Long> count(final TypedStateStoreSupplier<KeyValueStore<K, Long>> storeSupplier);

  • <W extends Window> KTable<Windowed<K>, Long> count(final Windows<W> windows,
                                                                                                   final TypedStateStoreSupplier<WindowStore<K, Long>> storeSupplier);

  • KTable<Windowed<K>, Long> count(final SessionWindows sessionWindows,
                                                                final TypedStateStoreSupplier<SessionStore<K, Long>> storeSupplier);
    
    

  • KTable<K, V> reduce(final Reducer<V> reducer,
                                       final TypedStateStoreSupplier<KeyValueStore<K ,V>> storeSupplier);
    
    

  • <W extends Window> KTable<Windowed<K>, V> reduce(final Reducer<V> reducer,
                                                                                                final Windows<W> windows,
                                                                                                final TypedStateStoreSupplier<WindowStore<K, V>> storeSupplier);
    
    

  • KTable<Windowed<K>, V> reduce(final Reducer<V> reducer,
                                                            final SessionWindows sessionWindows,

                                                            final TypedStateStoreSupplier<SessionStore<K, V>> storeSupplier);
    
    

  • <VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                                                         final Aggregator<? super K, ? super V, VR> aggregator,

                                                         final TypedStateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

  • <W extends Window, VR> KTable<Windowed<K>, VR> aggregate(final Initializer<VR> initializer,
                                                                                                               final Aggregator<? super K, ? super V, VR> aggregator,
                                                                                                               final Windows<W> windows,
                                                                                                               final TypedStateStoreSupplier<WindowStore<K, VR>> storeSupplier);

  • <T> KTable<Windowed<K>, T> aggregate(final Initializer<T> initializer,

                                                                        final Aggregator<? super K, ? super V, T> aggregator,

                                                                        final Merger<? super K, T> sessionMerger,

                                                                        final SessionWindows sessionWindows,

                                                                        final Serde<T> aggValueSerde,

                                                                        final TypedStateStoreSupplier<SessionStore<K, T>> storeSupplier);

• KGroupedTable - deprecate the following methods:

  • KTable<K, Long> count(final StateStoreSupplier<KeyValueStore> storeSupplier);

  • KTable<K, V> reduce(final Reducer<V> adder,
                                       final Reducer<V> subtractor,
                                       final StateStoreSupplier<KeyValueStore> storeSupplier);

  • <VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                                                         final Aggregator<? super K, ? super V, VR> adder,
                                                         final Aggregator<? super K, ? super V, VR> subtractor,
                                                         final StateStoreSupplier<KeyValueStore> storeSupplier);

• KGroupedTable - add the following replacement methods:

  • KTable<K, Long> count(final TypedStateStoreSupplier<KeyValueStore<K, Long>> storeSupplier);

  • KTable<K, V> reduce(final Reducer<V> adder,
                                       final Reducer<V> subtractor,
                                       final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier);

  • <VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                                                         final Aggregator<? super K, ? super V, VR> adder,
                                                         final Aggregator<? super K, ? super V, VR> subtractor,
                                                         final TypedStateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

• KTable - deprecate the following methods:
  • KTable<K, V> filter(final Predicate<? super K, ? super V> predicate, final StateStoreSupplier<KeyValueStore> storeSupplier);
  • KTable<K, V> filterNot(final Predicate<? super K, ? super V> predicate, final StateStoreSupplier<KeyValueStore> storeSupplier);

  • <VR> KTable<K, VR> mapValues(final ValueMapper<? super V, ? extends VR> mapper,
                                                           final Serde<VR> valueSerde,
                                                           final StateStoreSupplier<KeyValueStore> storeSupplier);

  • KTable<K, V> through(final String topic,
                                        final StateStoreSupplier<KeyValueStore> storeSupplier);

  • KTable<K, V> through(final StreamPartitioner<? super K, ? super V> partitioner,
                                        final String topic,
                                        final StateStoreSupplier<KeyValueStore> storeSupplier);

  • KTable<K, V> through(final Serde<K> keySerde, Serde<V> valSerde,
                                        final String topic,
                                        final StateStoreSupplier<KeyValueStore> storeSupplier);

  • KTable<K, V> through(final Serde<K> keySerde,
                                        final Serde<V> valSerde,
                                        final StreamPartitioner<? super K, ? super V> partitioner,
                                        final String topic,
                                        final StateStoreSupplier<KeyValueStore> storeSupplier);

  • <VO, VR> KTable<K, VR> join(final KTable<K, VO> other,
                                                      final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                                      final StateStoreSupplier<KeyValueStore> storeSupplier);

  • <VO, VR> KTable<K, VR> leftJoin(final KTable<K, VO> other,
                                                           final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                                           final StateStoreSupplier<KeyValueStore> storeSupplier);

  • <VO, VR> KTable<K, VR> outerJoin(final KTable<K, VO> other,
                                                               final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                                               final StateStoreSupplier<KeyValueStore> storeSupplier);

• KTable - add the following replacement methods:
  • KTable<K, V> filter(final Predicate<? super K, ? super V> predicate, final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier);
  • KTable<K, V> filterNot(final Predicate<? super K, ? super V> predicate, final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier);

  • <VR> KTable<K, VR> mapValues(final ValueMapper<? super V, ? extends VR> mapper,
                                                           final Serde<VR> valueSerde,
                                                           final TypedStateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

  • KTable<K, V> through(final String topic,
                                        final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier);

  • KTable<K, V> through(final StreamPartitioner<? super K, ? super V> partitioner,
                                        final String topic,
                                        final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier);

  • KTable<K, V> through(final Serde<K> keySerde, Serde<V> valSerde,
                                        final String topic,
                                        final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier);

  • KTable<K, V> through(final Serde<K> keySerde,
                                        final Serde<V> valSerde,
                                        final StreamPartitioner<? super K, ? super V> partitioner,
                                        final String topic,
                                        final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier);

  • <VO, VR> KTable<K, VR> join(final KTable<K, VO> other,
                                                      final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                                      final TypedStateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

  • <VO, VR> KTable<K, VR> leftJoin(final KTable<K, VO> other,
                                                           final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                                           final TypedStateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

  • <VO, VR> KTable<K, VR> outerJoin(final KTable<K, VO> other,
                                                               final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                                               final TypedStateStoreSupplier<KeyValueStore<K, VR>> storeSupplier);

• KStreamBuilder - deprecate the following method:

  • <K, V> GlobalKTable<K, V> globalTable(final Serde<K> keySerde,
                                                                     final Serde<V> valSerde,
                                                                     final String topic,
                                                                     final StateStoreSupplier<KeyValueStore> storeSupplier)

• KStreamBuilder - add the following replacement method:
  • <K, V> GlobalKTable<K, V> globalTable(final Serde<K> keySerde,
                                                                     final Serde<V> valSerde,
                                                                     final String topic,
                                                                     final TypedStateStoreSupplier<KeyValueStore<K, V>> storeSupplier)
• Deprecate Stores class
• Add a new replacement TypedStores class with the following extra public interfaces in addition to those equivalent to those in Stores class:

  • • Code Block

      public interface PersistentWindowFactory<K, V> { /** * Caching should be enabled on the created store. * @return the factory to create a persistent window store */ PersistentWindowFactory<K, V> enableCaching(); /** * Indicates that a changelog should not be created for the key-value store * @return the factory to create a persistent window store */ PersistentWindowFactory<K, V> disableLogging(); /** * Indicates that a changelog should be created for the store. The changelog will be created * with the provided cleanupPolicy and configs. * * Note: Any unrecognized configs will be ignored. * @param config any configs that should be applied to the changelog * @return the factory to create a persistent window store */ PersistentWindowFactory<K, V> enableLogging(final Map<String, String> config); /** * Return the instance of StateStoreSupplier of new window store. * @return the key-value store; never null */ TypedStateStoreSupplier<WindowStore<K, V>> build(); }

    • Code Block

      public interface PersistentSessionFactory<K, V> { /** * Indicates that a changelog should be created for the store. The changelog will be created * with the provided cleanupPolicy and configs. * * Note: Any unrecognized configs will be ignored. * @param config any configs that should be applied to the changelog * @return the factory to create a persistent key-value store */ PersistentSessionFactory<K, V> enableLogging(final Map<String, String> config); /** * Indicates that a changelog should not be created for the key-value store * @return the factory to create a persistent session store */ PersistentSessionFactory<K, V> disableLogging(); /** * Caching should be enabled on the created store. * @return the factory to create a persistent session store */ PersistentSessionFactory<K, V> enableCaching(); /** * Return the instance of StateStoreSupplier of new session store. * @return the key-value store; never null */ TypedStateStoreSupplier<SessionStore<K, V>> build();   }

    • differences in PersistentKeyValueFactory in TypedStores versus that in Stores:

      • PersistentWindowFactory<K, V> windowed(final long windowSize, long retentionPeriod, int numSegments, boolean retainDuplicates);

      • PersistentSessionFactory<K, V> sessionWindowed(final long retentionPeriod);

      • TypedStateStoreSupplier<KeyValueStore<K, V>> build();

    • differences in InMemoryKeyValueFactory in TypedStores versus that in Stores:

      • TypedStateStoreSupplier<KeyValueStore<K, V>> build();

 

Proposed Changes

Pull Request to demonstrate the changes: https://github.com/apache/kafka/pull/2992/files

The new usage would be e.g.:

TypedStateStoreSupplier<KeyValueStore<String, Long>> countStore = TypedStores.create("Counts")
    .withKeys(Serdes.String())
    .withValues(Serdes.Long())
    .persistent()
    .build();

TypedStateStoreSupplier<WindowStore<String, Long>> windowedStore = TypedStores.create("WindowedCounts")
    .withKeys(Serdes.String())
    .withValues(Serdes.Long())
    .persistent()
	.windowed(1000, 10000, 10, false)
    .build();

TypedStateStoreSupplier<SessionStore<String, Long>> sessionStore = TypedStores.create("SessionWindowedCounts")
    .withKeys(Serdes.String())
    .withValues(Serdes.Long())
    .persistent()
	.sessionWindowed(60000)
    .build();

Compatibility, Deprecation, and Migration Plan

Changes are intended to be backwards-compatible.

Test Plan

Only re-run of existing tests is envisaged at this time.

Rejected Alternatives

Add type parameters to current method parameters. This has been rejected as a backwards-incompatible change.

<K, V>If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.